Chang Zheng-5

New-generation heavy-lift orbital launch system, designed to loft space station modules, lunar and Mars probes, and heavy communications satellites into orbit. The launch vehicle is available in two basic configurations, the CZ-5 with a two-stage core vehicle and four strap-on boosters, and the CZ-5B with a single-stage core vehicle and four strap-on boosters.

Programme

China’s Long March 1/2/3/4 launch vehicles introduced between the 1970s and 1990s were all derived from the DF-5 (CSS-4) ICBM design. By adding a third-stage and four strap-on boosters, the launch vehicle’s payload capacity has been incrementally increased to about 10,000 kg to LEO, or 5,500 kg to GTO—almost the upper limit for the existing 3.35 m diameter vehicle design. While this was adequate for most satellite launch missions, the existing launch vehicles can not support China’s space ambitions to build a permanent Earth orbital station or send probes to the Moon and Mars.

As a result, the Chinese space industry has been seeking a ‘large rocket’ that could provide sufficient payload capability. The heavy-lift launch vehicle was a key aerospace system proposed under the 863 Programme, but it could only exist in concept as the Chinese space industry was unable to produce high-thrust rocket engines to power the launch vehicle. This finally changed in the 1990s when China acquired examples (and possibly design documents) of the Russian RD-120 liquid-fuel engine, which served as a template for China to develop its own new-generation engines.

Soon after 2000, the development for two major new series of rocket engines was approved by the Chinese government: the 120 t-thrust YF-100 high-pressure staged combustion cycle engine (including a smaller 18 t-thrust version YF-115) burning a LOX/Kerosene bi-propellant, and the 50 t-thrust YF-77 cryogenic engine burning the LOX/LH2 bi-propellant. In addition, a range of smaller upper-stages using both hypergolic and cryogenic propellants were also created.

As engine development proceeded, design work on the new-generation launcher family to be powered by these engines also proceeded in parallel. The original vision was ambitious: Chinese space engineers wanted to create three basic modular stages of 2.25 m, 3.35 m and 5.0 m diameter, powered by the YF-100 and YF-77 series engines. These modular stages can then be assembled into orbital launchers of various capabilities, all based on the common engine technology and rocket stage design. For example, the 3.35 m-diameter module powered by two YF-100 engines could serve as the strap-on booster for a heavy-lift launcher, but could also be used as the core vehicle for a medium-lift launcher.

However, this modular approach was eventually abandoned and instead three separate series of orbital launchers were developed: the 2.25 m-diameter (with a first-stage of 3.35 m diameter) small-load CZ-6, the 3.35 m-diameter medium-load CZ-7, and the 5 m-diameter heavy-lift CZ-5. Despite the abandoning of the modular approach, the three launcher series share common rocket engines with the YF-100, YF-115 and YF-77.

The development of the new-generation orbital launchers was not merely introduction of new launch vehicle designs, but also an overhaul of China’s aerospace manufacturing and orbital launch facilities. The payload capability of China’s existing generation launchers has reached a ceiling due to a single factor of logistics: as China’s three existing launch sites are all located inland, launcher components have to be transported from their factory to launch sites by railway. The size of the launcher is limited to 3.35 m in diameter and about 14 m in length. Any design bigger than these dimensions will not fit through the railway tunnels.

To overcome this limit, new rocket and spacecraft fabrication and test facilities have been constructed in Tianjin on the eastern coast of China mainland. At the same time, a brand new space launch centre with two launch complexes have been built at Wenchang, Hainan Island. Launcher components are transported from their manufacturing factory to the launch site by two specially-built Yuanwang sea-going cargo ships.

Development

The CZ-5 development project gained governmental approval in June 2004, with the aim to introduce a heavy-load orbital launcher capable of lofting 14 tonnes of payload to Geostationary Transfer Orbit (GTO), or 25 tonnes to Low Earth Orbit (LEO). The development contract was awarded to China Academy of Launch Vehicle Technology (CALT), with Shanghai Academy of Spaceflight Technology (SAST) sharing some development tasks. The development featured a whole range of new technologies not seen on previous Chinese launcher designs, including new engines, digital flight control system, computer-aided 3D design methods, software model testing, and new welding techniques.

Both YF-100 and YF-77 have encountered great technical challenges, causing significant delays to the CZ-5 development. It took the Chinese space industry nearly two decades to fully digest the RD-120 technology and produce its own designs. In May 2012, the YF-100 engine was successfully tested at 7103 Factory of the Xi’an-based Academy of Aerospace Propulsion Technology (AAPT) to 20,000 revolutions per minute for 200 seconds, reaching a temperature of 3,000°C. This allowed the engine to be certified for design finalisation, making China the second country in the world after Russia to have grasped the high-pressure staged combustion cycle rocket engine technology.

The original CZ-5 design proposed six variants (A to E), using the 5 m diameter core stage and different combinations of strap-on boosters and an upper stage to achieve different payload capacities. However, only two variants have been developed: the basic variant two-stage CZ-5 designed for GTO missions, and the single-stage CZ-5B designed for LEO missions. Both variants are fitted with four strap-on boosters of 3.35 m diameter.

The first test flight of the CZ-5 was originally scheduled for late 2014, but this date has slipped to November 2016. The CZ-5 (Y1) mission was originally scheduled for 18:00 CST (10:00 UTC) on 3 November 2016, but a string of technical glitches on the new rocket including liquid oxygen leaks, propellant tank cooling failure, and flight control problems caused four holds during the launch countdown. The launch time was postponed twice to 20:40 CST. The launch vehicle eventually lifted off at 20:43:13, slightly later than the originally scheduled launch window of 18:00—20:40. There were further anomalies during the flight but the payloads were placed close enough to their intended orbits.

The Long March 5 (Y2) launch vehicle rolled out of production line and was delivered to Wenchang Space Launch Centre in late April this year. After a three-month checkout procedure, the assembled launch vehicle and payload stack was rolled out atop the mobile launcher platform to Launch Complex 101 on 26 June. The launch window was finalised as 2 July, with the fuelling of the propellants on the launch pad beginning at 16:30 CST (08:30 UTC) on 1 July.

At 19:23:23 CST (11:23:23 UTC) on 2 July, the Long March 5 (Y2) launch vehicle carrying the Shijian 18 technology demonstration satellite lifted off from its launch pad. The launch mission appeared to have gone as scheduled, with the commentators on live television confirming everything was normal throughout the initial flight. However, the live TV broadcast came to an abrupt end shortly after the second-stage’s first engine cu-off to enter coast phase. Soon after, the Chinese state media finally confirmed that the launch mission had failed.

It was later revealed that trouble began shortly after the lift-off, with telemetry data showing an anomaly with one of the two cryogenic YF-77 engines in the core vehicle’s first-stage. The underpowered launch vehicle soon began to deviate from the planned ascent trajectory, and the first-stage was jettisoned at a much lower altitude than planned. As a result, the second-stage could not gain enough delta-v to enter orbit before its engine shut down. The stage and its payload re-entered the atmosphere over the Pacific.

Design

The basic variant CZ-5 is in a configuration of two-stage core vehicle (5 m diameter) plus four strap-on boosters (3.35 m diameter), giving a payload capacity of 14,000 kg to GTO. The launch vehicle is 56.97 m in length, with a gross mass of 869 t and lift-off thrust of 10,573 kN.

First-Stage and YF-77 Engine

The first-stage of the CZ-5 is 31.02 m in length and 5 m in diameter, with a gross mass of 175.8 t. The stage comprises (from front to rear): oxidiser tank, inter-tank ring section, fuel tank, engine frame, and tail section. The front end of the forward oxidiser tank is protected by a fibreglass heat insulation layer to prevent damage from the high pressure and hot stream of engine exhaust from the second-stage engine during stage separation.

The stage is powered by two single-chamber YF-77 engine rated at 50 tonnes (510 kN) each at sea-level, or 70 tonnes (700 kN) in vacuum. Each engine can swing independently in two planes to provide directional thrust and steering for the launch vehicle. The two main engines are mounted on the engine frame secured to the rear of the fuel tank. The frame transfers the thrust of the engines to the vehicle’s thrust and weight bearing load structure.

The YF-77 is China’s first high-thrust cryogenic rocket engine, burning liquid hydrogen (LH2) as fuel and liquid oxygen (LOX) as oxidiser. Unlike some of the most advanced cryogenic rocket engines in the world, which all use staged combustion cycle, the YF-77 uses less efficient gas-generator cycle, resulting in an inferior performance compared with foreign designs of the same class.

Strap-on Boosters and YF-100 Engine

The four strap-on boosters of the CZ-5 provide most of the initial thrust during during ascent. Each booster is 3.35 m in diameter and 26.28 m in length, and consists of oxidiser tank, inter-tank ring section, fuel tank, engine frame, and tail section. An aerodynamic nose is attached to the front end of the booster covering the upper bulkhead of the liquid oxygen tank.

Each booster is powered by two single-chamber YF-100 engines, producing a total thrust of 2,680 kN at sea-level. The engines can be pivoted at radial direction to provide additional directional thrust and steering for the launch vehicle. The two engines are mounted on the engine frame secured to the rear of the fuel tank. The frame transfers the thrust of the engines to the vehicle’s thrust and weight bearing load structure.

The YF-100 is a pump-fed staged combustion cycle liquid engine burning the LOX/kerosene bi-propellant, with adjustable thrust and variable mixture ratio. The engine’s pre-burner burns all the LOX mass flow with a low volume of kerosene to generate hot gas that powers the single turbine. The turbo-pump is a single-shaft design, with a single-stage oxygen pump and a dual-stage kerosene pump driven by the same turbine. It also has two low-pressure pumps that prevent cavitation. The engine has a heat exchanger to heat oxygen gas for LOX tank pressurisation, and also supplies high-pressure kerosene as hydraulic fluid for the thrust vector control actuators.

Second-Stage and YF-75D Engine

The second-stage maintains the overall diameter of the first-stage at 5 m and comprises (from front to rear): instrument compartment, oxidiser tank, inter-tank ring section, and fuel tank. The engines are directly mounted on the rear of the fuel tank. The instrument compartment at the front houses the flight control system, navigation platform, and gas canisters.

The stage is powered by two single-chamber YF-75D engines, each rated at 78 kN in vacuum. The YF-75D was developed from the YF-75 liquid cryogenic rocket engine used by the CZ-3A series launchers, burning liquid hydrogen (LH2) as fuel and liquid oxygen (LOX) as oxidiser in a closed circuit expander cycle. Each engine can swing independently in two planes to provide directional thrust and steering. Both the combustion chamber and hydrogen turbine of the YF-75D have been redesigned to achieve better performance.

YZ-2 Upper Stage

The YZ-2 (Yuan Zheng-2, “Expedition 2”) is a new upper stage specifically designed for use on the CZ-5. Developed by China Academy of Launch Vehicle Technology (CALT), the upper stage serves as a “space tug” to deliver spacecraft vehicles and satellites directly into their intended orbit without the need to use their own propulsion.

The upper stage is 5.2 m in diameter and weighs 1.8 t, with multiple re-ignitions and precision control capabilities. With its own propulsion, navigation and control systems, the YZ-2 upper stage is capable of flying a complex mission profile autonomously, performing a series of orbital manoeuvres to deploy its payloads at different altitudes and on different orbital planes.

Payload Fairing

The payload fairing of the CZ-5 is 5.2 m in diameter and 12.5 m in length.